revert writer won't allow us to enter multiple CrossRefBookmark

i.e.

commit af64f430181088460d5c574683dd1fdfd377ebcd
Date:   Mon Dec 8 16:11:41 2014 +0000

    writer won't allow us to enter multiple CrossRefBookmarks on the same node

    e.g. fdo63164-1.docx and loads more like that, and the .docx genuinely has
    multiple bookmarks at the same place, so just allow the first one and discard
    the following ones

in favour of

commit 7a12360e1f2c0a5bc0927131a750740d35cfd1ab
Date:   Wed Dec 10 14:56:27 2014 +0100

    sw: don't assert when SwXBookmark creates duplicate CrossRef*Bookmark

    The bugdoc of fdo#87110 has a couple such duplicates.  Check for it and
    let SwXBookmark throw an IllegalArgumentException.

but leave test doc in place

Change-Id: Ib0bfc991684b2c9c4f1959a17c49bf1c0179be79